fix(tui): fail closed for stale auto review metadata

[shiny-code-bot]

Summary

• fail closed when in-flight Auto Review status/completion events omit required session or snapshot metadata
• prevent pre-start terminal agent status from surfacing findings before the review run proves it belongs to the active session
• add targeted regressions for missing metadata, pre-start terminal status, and metadata-free finish events

Validation

• cargo test -p code-tui --features test-helpers auto_review
• ./build-fast.sh

Refs #76